The wire enamels commonly employed today are in general solutions of the typical wire enamel binders, for example polyesters, polyesterimides and polyurethane resins, in organic solvents, alone or in combination with customary commercial hydrocarbon cuts. For use on wires of small to medium diameter, these enamels are available on the market in a sufficiently good quality. Wire enamels employed for the coating of thick round wires or for profiled wires, on the other hand, are subject--compared to the standard enamels--to particularly stringent requirements regarding the adhesion.
Polyesterimide enamels employed for wire coating are known, for example, from DE-A 1445263 and 1495100 and also WO 91/07469 (PCT-EP 90/01911). Because of their good mechanical, thermal and chemical properties they have found broad application in the coated-wire industry. In this case the polyesterimides are prepared in a known manner from polyols, polycarboxylic acids or derivatives thereof and imide-forming components. In general, such wire enamels satisfy the abovementioned stringent requirement regarding the adhesion to thick round or profiled wires only to a limited extent.
Likewise known are polyamideimides, used as binders for wire coating, which are described, for example, in U.S. Pat. No. 3,554,984, DE-A-24 41 020, DE-A-25 56 523, DE-A-12 66 427 and DE-A-19 56 512. Again, such polyamide-imide wire enamels only go a certain way toward meeting the abovementioned requirements regarding the adhesion.
The prior art has also disclosed polyimides which comprise polyoxyalkylenediamines as molecular building blocks.
In U.S. Pat. No. 4,116,937 Jeffamine.RTM. ED 900, an amine-terminated polyethylenepolypropylene glycol, is converted to a bismaleimide by reaction with maleic anhydride. In a formulation which also includes other bismaleimides, the material is extruded, in a complex procedure, onto a copper conductor and is cured at from 300 to 400 degrees F. A procedure of this kind is unsuitable in practice for the coating of wires. EP-A-0 329 833 describes the preparation of a hotmelt adhesive from an adduct of polyoxyalkylenediamine and trimellitic anhydride with an alkylenediamine. Such hotmelt adhesives are unsuitable for the coating of wires.
EP-A-0 281 003 describes a flame-resistant elastomer for injection molding applications, comprising a reaction product of an adduct of polyoxyalkylene diamine, alkanediol, trimellitic anhydride and dimethyl terephthalate and of melamine. Comparable reaction products without the melamine reaction component are described in EP-A-0 270 790. A synthetic rubber consisting of the reaction product of polyoxyalkylenediamine, trimellitic anhydride, a dimeric fatty acid and 1,4-butanediol is described in U.S. Pat. No. 4,544,734. The rubber has good thermal properties, is chemically resistant and can be extruded. In Journal Appl. Polym. Sci. (1982), 27 (11), pages 4295 to 4311, finally, a polyimide is described which likewise comprises polyoxyalkylenediamine as monomeric building block.